Skype does not work via Checkpoint proxy server

Hello guys, can you help me. i use my checkpoint as a corporate non-transparent http/https proxy server. and my users cannot use Skype application via this proxy server. i allowed "All recognized" access for skype user. but skype still does not work.

Also, the SYN packet should not be on port 55980, which makes me wonder about the Skype configuration. These are the ports required by Skype:

443/TCP

3478-3481/UDP

49152-65535/UDP + TCP

The SYN packet should be on TCP 443, and once the three way handshake has been established, then a high port is used for the conversation stream, which should be 49152-65535 UDP. Ports 3478-3481 are for directory and status updates, not the media stream. Since RTP is a UDP protocol (and thus stateless) the SYN packet message in the tcpdump applies to the connection to Skype, not the conversation stream.